webpy lighttpd and flup. 500 error

Question

Currently I have a lighttpd server with flup and webpy. If you make enough requests fast enough (say clicking a link repeatedly many times or doing an apache bench) Lighttpd throws a 500 internal server error. At this point it is pretty easy to exploit (I can break it with several clicks of a link).

Lighttpd code:

fastcgi.server = (
    "/sm" => (
      ( "host" => "127.0.0.1",
        "port" => 7000,
        "check-local" => "disable",
      )
    )
)

And the error in my lighttpd error logs:

2012-11-09 16:17:32: (mod_fastcgi.c.3005) got proc: pid: 0 socket: tcp:127.0.0.1:7000 load: 15 
2012-11-09 16:17:32: (mod_fastcgi.c.2494) unexpected end-of-file (perhaps the fastcgi process died): pid: 0 socket: tcp:127.0.0.1:7000 
2012-11-09 16:17:32: (mod_fastcgi.c.3325) response not received, request sent: 1252 on socket: tcp:127.0.0.1:7000 for /sm , closing connection 
2012-11-09 16:17:32: (mod_fastcgi.c.1515) released proc: pid: 0 socket: tcp:127.0.0.1:7000 load: 14 

This makes me feel like lighttpd is breaking because flup didn't respond. Now, I can simply throw more threads at the problem and it goes away (or at least makes it harder to exploit). flup server code:

#!/usr/bin/python

from apps.main import app as main_app

# run as fastcgi
from flup.server.fcgi import WSGIServer
params = {
    'multiplexed': False,
    'bindAddress': ('127.0.0.1', 7000),
    'maxThreads': 9,  <---- If I move this up to 20 no more problems
}
server = WSGIServer(main_app.wsgifunc(), **params)
server.run()

Another reason I think this is a flup problem is because I can bypass the flup server and just do a proxy that sends requests directly to webpy and I don't have the problem. Now, I would rather not just up the threads if there is a more elegant solution out there. Does anyone know what could be causing flup to break? Or are my conclusions thus far misplaced?